1. Field of the Invention
The present invention relates to a semiconductor device having a semiconductor chip being connected onto a surface of a printed wiring board in a flip-chip connection.
2. Description of the Related Art
In a structure in which a semiconductor chip is connected onto a printed wiring board in a flip-chip connection, in order to ensure the reliability of a connection of the chip with the printed wiring board, a gap formed between the chip and the board is filled with an underfill (sealing resin) so as to reinforce a connection of the chip with the printed wiring board. In order to enhance the reinforcing effect, the underfill is made to overflow a little from between the chip and the board to the periphery so that the overflowed underfill is formed into a mountain-shape, the top of which is the chip and the skirt portion of which is extended from the top of the mountain-shape. However, in a case of a structure in which components are high-densely mounted on the board, another device or a wiring system, etc., is arranged very close to the chip. Therefore, it is necessary to prevent the occurrence of such a problem that an overflowing underfill widely spreads and reaches a periphery portion, which negatively affects an electric operation of the semiconductor device. Accordingly, in order to restrict an outflow range of the underfill overflowing from between the chip and the board, various proposals have been made until now.
JP-A-5-183070 and JP-A-9-162208 disclose a structure of a dam, which surrounds a semiconductor chip in a frame shape, for restricting an outflow range of the sealing resin (not referred to as an underfill), in which not the flip-chip connection but a wire bonding connection is used. Since this structure uses the wire bonding connection, as compared with the structure in which the flip-chip connection is used, sizes of the wiring board and the dam are large. However, both the chip connecting structures have a basic concept in common in which the outflow range of the resin is restricted by the dam.
In order to enhance an effect of restricting the outflow range, JP-A-5-183070 proposes a dam in which multiple layers are three-dimensionally laminated, and JP-A-9-162208 proposes a dam which is double frame shaped two-dimensionally.
In order to restrict an outflow range of the underfill in a structure in which the flip-chip connection is used, JP-A-2001-244384 makes the following three proposals: (1) A step structure in which a solder resist layer is made to be thinner for one step than an original solder resist layer, for all over the circumference of the chip from a periphery edge of a chip connecting region to a periphery region; (2) A structure in which a groove surrounding the overall circumference of a chip is formed in a solder resist layer in a periphery of a chip connecting region; and (3) A structure in which a frame-shaped dam surrounding the overall circumference of a chip is formed on a solder resist layer in a periphery of a chip connecting region.
However, an outer shape and a thickness of the semiconductor device have been recently reduced. Accordingly, components as the inner structure have been high-densely mounted and miniaturized. Therefore, it is difficult for these methods to reliably restrict an outflow range of the underfill.
FIG. 1 is a schematic illustration showing a portion of a semiconductor device 10 having a semiconductor chip 14 connected onto a printed wiring board 12 in a flip-chip connection. On a surface of the printed wiring board 12, a frame-shaped dam 16 for restricting an outflow range of the underfill surrounds an entire circumference of the semiconductor chip 14, and solder balls 18, which are external connection terminals for connecting the semiconductor chip 14 with the external circuit via a wiring pattern, are arranged outside the frame-shaped dam 16.
In the case where the solder balls 18 are arranged on a surface of the printed wiring board on the side on which the chip 14 is mounted, the solder balls 18 are arranged very close to the chip 14. Therefore, a flow of the underfill overflowing the dam 16 easily reaches the solder balls 18.
In some cases, as a customization of a basic design, the solder ball is further disposed in a portion very close to the corner of the semiconductor chip. In this case, an space between the outer edge of the semiconductor chip and the inner edge of the dam is reduced. Accordingly, there is a high possibility that a flow of the underfill overflowing from between the chip and the printed wiring board goes over the dam and overflows outside.
FIG. 2A is an enlarged view of the corner portion which is surrounded by a circle C drawn by a broken line shown in FIG. 1. As shown by the reference numeral 20 in the drawing, the underfill, which is filled in a gap between the semiconductor chip 14 and the printer wiring board 12, flows outside from a mounting region of the semiconductor chip 14. However, an outflow range of the underfill shown by a reaching front edge 20F is restricted inside the frame-shaped dam 16 surrounding the semiconductor chip 14.
FIG. 2B is a view showing a state in which customization is made in such a manner that the solder ball 18A is further disposed in the corner portion. In the corner portion, in order to ensure an area required for the further disposed solder ball 18A itself and clearance in the periphery of the solder ball 18A, the dam 16 is arranged being retreated to the semiconductor chip 14 side. Therefore, a space between the outer edge of the semiconductor chip 14 and the inner edge of the dam 16 is reduced. As a result, the front edge 20F of the underfill 20 is forcibly dammed up at a position of the dam 16 that is retreated as compared to the original reaching position 20F′ shown by the broken line in the drawing. Accordingly, the underfill 20 is locally collected and raised. Consequently, there is a high possibility that the underfill 20 goes over across the dam 16 and overflows.